In 2016, Gelula made her film debut as the lead actress with romantic drama film First Girl I Loved, directed by Kerem Sanga. The film premiered at the 2016 Sundance Film Festival and won the audience award for Best Of NEXT. Gelula's performance in the film as Anne received rave reviews from various critics.[2]

Gelula began her acting career at the age of 10 as an extra in the M. Night Shyamalan film Lady in the Water, which she later revealed neither she nor her parents ever viewed. Two years after, in the sixth grade, she found a manager. Before moving to Los Angeles, her agent in New York got her an audition for the role of Jean Fordham in an Arden Theatre Company production of August: Osage County, directed by Terry Nolen, which she ended up starring in.[8] She recalls remembering originally trying to turn down the part, but later realizing that she was very interested in it.[3]

When Gelula initially auditioned for the role of Xanthippe on Unbreakable Kimmy Schmidt, she was in Los Angeles, but casting was only happening in New York City. She gave the crew of the show an audition tape, and received a call one month later that they were interested in her for the part. The crew asked her to do a table read with the cast before she was given the part, and she eventually received the role. She claims she does not know why the character of Xanthippe was given the name she was given.[9]